The proposed research aims to study, in mouse tumor models, the effects of radiation therapy on tumor growth and on concomitant, established tumor immunity, to reveal fundamental aspects of anti-tumor immunity, and to indicate safe and hazardous procedures in radiation therapy of antigenic tumors. Areas of investigation are primarily four: 1. A study to determine whether the tumor growth enhancing side effects which may follow therapeutic radiation have immunological and/or non-immunological bases. 2. A study to determine the relative risks of immunological impairment when specific organs or anatomical regions are in the radiated field, and to evaluate the balances of risk versus benefit when tumor cells exist both inside and outside the radiated field. 3. A comparative study to determine the dosimetry of therapeutic effects of radiation vis-a-vis the dosimetry of immunological impairment induced by radiation. A part of this study will be to develop the kinetics of the induction of immunological impairment and its duration following various conditions of radiation. This study will also test the prophylactic use of low dose radiation against occult secondary tumor growth suspected in specific organs or anatomical regions. 4. A study of procedures which may prevent, limit and repair radiation-induced damage to host anti-tumor immune resistance. The effects of radiation therapy on anti-tumor immunity will be assayed in treated animals by challenges of implants of living tumor cells. The challenges will use s.c. and i.p. implantation and will also use intravascular implantation to study the effects of radiation under conditions simulating metastatic spread of tumor growth. To study the effects of radiation on cellular and on humoral immune factors separately, cells or serum from radiation treated mice will be passively transferred to normal or irradiated (400R) unsensitized recipients at the time when the recipients are challenged with implants of living tumor cells. To try to repair radiation induced damage of immune resistance, serum and/or lymphoid cells or lymphoid cell fractions will be transferred from immunized donors to radiation treated recipients.